A memory card with a memory chip built therein has been known as one of recording media for storing information. Since the memory card is excellent in portability, it has been widely used as a recording medium of portable electronic devices such as a portable information terminal or a cell phone.
These portable electronic devices have been downsized and increased their memory capacity year by year in order to improve the portability. This market trend requires the memory card to be downsized and have a greater capacity. In general, the memory card is specified its shape, size, and thickness by the industry standard, so that the memory card must meet this standard before it achieves the greater capacity.
To meet the foregoing requirements, a plurality of boards on which memory chips are mounted is layered on one face of a base board, and a control chip for controlling the operation of the memory chips is mounted on the other face thereof. This structure allows increasing a capacity of the memory card. This technique is disclosed in, e.g. patent document 1.
Here is another technique: On a memory chip mounted on a lead frame, another memory chip is layered but shifted therefrom. The electrodes of these two memory chips and an electrode of a control chip mounted on the lead frame are coupled to the lead frame via a gold wire, so that the thickness of the memory card can be reduced. This technique is disclosed in, e.g. patent document 2.
However, the memory card disclosed in patent document 1 is limited to decrease its thickness because of the following reason: The memory chips and the control chip are mounted on different faces of the base board, and the memory boards on which the memory chips are mounted are layered together.
The memory card disclosed in patent document 2 has some restrictions: The memory chips and the control chip are mounted onto the board by a wire bonding method, so that the chips, wires, and lead frame need to be sealed with thermosetting resin after they are mounted. At this time, a sealing layer is to be thick enough for covering the memory chips and the wires, so that the memory card is limited to be downsized or to be thinner. Since a sealing step is needed in addition to the mounting step, a reduction in the manufacturing cost is limited. On top of that, the quality of mounting of respective chips cannot be inspected before all the chips are mounted to the lead frame, so that if parts of chips are defective, they cannot be detected before all the chips are mounted. The manufacturing cost is thus obliged to increase.    Patent document 1: Unexamined Japanese Patent Publication No. 2003-108963    Patent document 2: Unexamined Japanese Patent Publication No. 2004-13738